I need inner_holder to have width of 960px and I need it to be centered. I tried using width: 960px and margin: 0px auto but it doesn't work. How can I center the divs inside inner_holder?
HTML:
<div class="parent_container">
    <div class="inner_holder">
        <div class="column column1">
            <div class="inner_clip"></div>
        </div>
        <div class="column column2">
            <div class="inner_clip"></div>
        </div>
        <div class="column column3">
            <div class="inner_clip"></div>
        </div>
    </div>
</div>
CSS:
.parent_container {
      height: auto;
      margin: 15px auto;
      min-height: 500px;
      width: 960px;
}
.column {
     float: left;
     margin-right: 50px;
}
.inner_clip {
    background-color: #333333;
    height: 250px;
    margin-bottom: 20px;
    width: 250px;
}